This invention is directed to a UV radiation system having a material for increasing the ratio of desirable radiation to undesirable radiation to a target provided by a radiation source.
In the field of UV sterilization or disinfection, the typical target media is a durable (non-absorbing, non-degenerating) material such as metal, ceramic or chemically simple solutions like water or saline, and the energies involved are typically low, that is, less than 0.1 J/cm2 per pulse total radiation or 20 Watts/cm2 for a continuous radiation source.
The use of a high energy broad spectrum radiation source to inactivate microorganisms has been disclosed in the prior art. U.S. Pat. Nos. 5,768,853; 5,786,598; 5,034,235; 4,871,559; and 5,900,211; and WO96/09775 have disclosed the use of a broad spectrum radiation source to inactivate microorganisms on food, water and medical devices. For the applications of the broad spectrum radiation source, damage to the exposed articles, such as the food, water, and medical devices by the radiation has not been considered. U.S. Pat. Nos. 5,768,853 and 5,900,211 suggest that the cooling fluid around the flash lamps can be replaced with a liquid for cooling and/or spectral filtering by the use of selected liquid solutions with desired spectral transmittance/absorbance characteristics. No materials other than water are suggested for the spectral filtering liquid, nor is there any discussion of which ranges to filter and/or for what purpose. U.S. Pat. No. 5,768,853 discloses that the outer safety glass of one of the described embodiments does filter out wavelengths shorter than 200 nanometers (nm) to prevent the formation of ozone outside the outer safety glass, although the composition of the glass is not disclosed.
WO 97/33629 discloses a method of sterilization and purification of biological sera and other contaminated fluids through the deactivation of pathogens by exposing them to a precise spectra of UV radiation. The precisely controlled spectra of radiation is specific to the molecular make-up of the pathogens to kill them, but leaves the surrounding cells, proteins, and other components intact. The biological sera are irradiated with UV radiation from about 200 nm to about 250 nm. The specific wavelengths that provide optimal kill of each virus, bacteria or other microorganism is determined within a narrow range of from 3.0 to about 10.0 nm, preferably 3 to 5 nm. A transmitter/regulator, grating or other optical filter can be used to control the wavelength size and variation, but there are no specific examples described. The exposure cell window where the sera is placed is made of quartz, sapphire or UV grad fused quartz silica and can be coated with a transmission material such as polytetrafluorocarbon which allows the UV radiation wavelength to pass through unadulterated. Teflon may also be used as a UV transparent disposable lining.
EPO 0277505 B1 discloses a UV radiation lamp, which is used for sterilizing bottles. The lamp has a reflector, referred to in the patent as a mirror which has a dielectric coating. The dielectric coating (dichroic or interference filter) is used to achieve selective reflection of UV radiation. The reflector can be coated with several tens of dielectric layers each having a thickness of a quarter of the wavelength of the radiation. Suitable materials for the dielectric coating include AL2O3/NaF, Sc2O3/MgF2, ThF4/Na2AlF6, HfO2/SiO2, and PbF2/Na3AlF6. Dielectric coatings are suitable for low energy absorption of UV radiation, but will not survive the demands of a high energy system, and will have short effective lifetimes in a high energy system. Further, dielectric filters are extremely angle sensitive, so they will not be effective for a shaped reflector, which changes the angle of incidence at the filter.
Lamp manufacturers often add dopants to the lamp envelope in a lamp to extend the life of the lamp. Depending on the lamp and what it is to be used for, some dopants are selected to cut off UV radiation entirely, e.g. cerium oxide in the lamp envelope of flash lamps used in laser applications. Other dopants are selected to cut off that portion of the UV radiation less than 180 nm which creates ozone. Lamps having these dopants are called xe2x80x9cozone-free bulbs.xe2x80x9d Other dopants are added to the lamp envelope to strengthen the lamp envelope against thermal shock.
For the application of high energy UV radiation to a polymeric medical device, the inventors have determined that damage to the medical device due to the radiation exposure must be considered, because it may render the exposed medical device useless for its intended purpose. There is a need for materials and ways to incorporate the materials into the lamp system to attenuate the undesirable portion of the UV radiation which is damaging to the polymeric medical device without reducing or significantly reducing the desired portion of the UV radiation, e.g. germicidal effective radiation.
This invention provides a high energy radiation system which produces UV radiation comprising a selectively attenuating material which increases the ratio of desired to undesired radiation to reduce the radiation damage to a target by selectively attenuating at least 30 percent of the radiation from 180 up to 240 nm which impinges upon said attenuating material, and directs greater than 50 percent of the radiation from 240 nm and 280 nm which impinges upon said attenuating material.
The radiation system comprising attenuating materials which selectively attenuate the radiation make it possible to expose to high energy UV radiation targets which are sensitive to UV radiation from 180 nm up to 240 nm. These high energy UV radiation systems produce radiation, which is undesired and desired. Without attenuation, the undesired UV radiation damages the materials of or changes the characteristics of a target at the same time the desired UV radiation is delivered. The target can be any material which comprises UV-sensitive composition(s). Damage to the target includes color changes of organic or inorganic dyes, chain scissions or alteration of the mechanical properties of polymers or other organic materials, or causing oxidation of organic materials. By selectively attenuating the undesired radiation, it is possible to use a high energy UV radiation system on products including organic products and inorganic products which would otherwise be damaged by the radiation, or to treat a broader class of materials, some of which have a low threshold for damage when subjected to the undesired radiation. This invention also simplifies the process control for the radiation systems used to expose UV-sensitive targets, because the amount of undesired radiation delivered after attenuation can be tailored to be below or much below the threshold for damage to the target, which will give more leeway in the amount of radiation which can be delivered. In the preferred embodiments, this invention is used to treat polymeric contact lenses in solution in polymeric packaging. The UV radiation damages the contact lens polymers, container polymers and solution additives. The invention will be described in reference to polymeric target materials; however, it is understood that additional UV-sensitive target materials could be treated by the method of this invention. One important application for this invention is in a lamp system for lasers wherein the target material is the laser medium, e.g. laser dyes, or other organic medium, which is sensitive to UV radiation.